HP 209A Oscillator Stuck Fine Tuning Knob

[Johnny10]

Hey Guys,

I have project I am working  on and wondered if I could get some input on these locked tuning knobs.

The fine tuning knob was locked tight.

I applied some penetrating oil to the shaft  but can only get this shaft to rotate with a pair of vice grips. Replacing the knob just leaves it impossible to turn.

Is there a lubricant that will get in there and loosen this shaft?


Had a similar problem on a HP Sweep Oscillator of same vintage, that knob stayed a bit stiff after unlocking but it could be moved.

[Tomorokoshi]

I've encountered different types of greases over the years in different equipment. Not sure what is in this one.

Some of the grease I've had to clean up almost turned into a tar, and it couldn't be cleaned until the parts were separated. This may be a case of letting it slowly work over the course of a week or two. As you can see the shaft can get galled by the vice grips.

Can the shaft be pushed out from the back if that inside cover and the main dial are removed? That's how other signal generator "fine" knobs were constructed in similar vintage equipment.

Otherwise depending on the situation I've used:
91% alcohol
WD-40
"Orange" cleaner
One of those Super Penetrating Oil things
"Electronics" spray cleaner (check for paint and plastic compatibility)
Automotive electrical cleaner (don't, damages paint and plastics)
Brake cleaner (don't, damages paint and plastics)